The present invention relates to a bicycle and, more particularly, a traction system for driving both wheels of a bicycle.
Traction at both wheels of a bicycle permits better transmission of the applied forces in order to permit greater ease of travel on slippery surfaces, for instance, for locomotion over iced or snow-coated surfaces, or when crossing a river on the bottom of which there may be slippery stones, etc. The two-wheel traction system makes it possible for the force applied to the pedals to be transmitted more gently and progressively, with larger gripping surface and with greater certainty of locomotion, eliminating the dangers of uncontrollable slippage of the rear wheel.
A traction system in accordance with the present invention can be applied to any type of bicycle with a gearshift, but is specifically advantageous for mountain bicycles. As is conventional, the bicycle includes a system or set of pedals of traditional construction as well as a gearshift consisting of a set of gears mounted on the axle of the rear wheel and driven by a main drive chain connected to the pedals.
In accordance with the present invention, the traction system comprises first and second auxiliary traction chains and a flexible intermediate transmission.
In one embodiment of the invention, the first auxiliary traction chain is mounted between the innermost sprocket of the gearshift and a first independent idler sprocket, the second auxiliary chain is mounted between a sprocket which is rigidly attached to the axle of the front wheel and a second independent idler sprocket, and the flexible intermediate transmission is connected between the first and second idler sprockets of the auxiliary chains.
The innermost sprocket of the gearshift is separated from the rest of the sprockets of said gearshift by a separation stop with a safety protector, thus preventing the danger of contact between the main drive chain and the first auxiliary traction chain.
The flexible intermediate transmission is formed of rigid and flexible shafts which are connected to each other and to transmission housings connected to the first and second auxiliary chains by cardan joints.
The first independent idler sprocket and a transmission associated with the sprocket are mounted on the tube of the frame which supports the seat. The second independent idler sprocket and a transmission associated with the sprocket are mounted on a support which is fastened to the front fork.
The arrangement of the different parts described will be better understood from the following description, given with reference to the accompanying drawings showing one exemplary embodiment.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.